In our news wrap Monday, a bombing in Bangkok has killed dozens and injured more than 100. Also, a cyber-attack on the IRS was far worse than originally believed: more than 330,000 taxpayer accounts may have been accessed in a breach last May.

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JUDY WOODRUFF:

It turns out that a cyber-attack on the Internal Revenue Service was far worse than first thought. The agency announced today an additional 220,000 taxpayer accounts were potentially accessed in the breach last May. That brings the total affected to more than 330,000. The IRS says the hackers, possibly from Russia, wanted stolen identities in order to claim fraudulent refunds.

China has dismissed a warning from President Obama about its agents operating secretly in the U.S. The New York Times reported the Chinese are pressuring expatriates wanted for graft and corruption to return home. China's state news agency called the American warning a — quote — "regrettable move."

A bomb blast rocked Thailand's capital city today during evening rush hour. Reports of the dead ranged from 18 to 27, possibly including foreigners, with more than 100 injured.

Dan Rivers of Independent Television News reports.

DAN RIVERS:

At the height of rush hour, a fire ball engulfs one of Bangkok's busiest crossroads. Caught on the dashboard camera of a car nearby, the explosion could be heard across the city.

The blast hit the city's famous Erawan Shrine, where Thais pray for good luck. Tonight, though, it was transformed into a scene of carnage. The emergency services arrived moments after the attack, helping the dozens of people caught up in the mayhem, many still shaking with shock.

Bodies were strewn across the street, just yards from several five-star hotels and shopping malls popular with foreign tourists. Early reports suggested it was a motorbike bomb, but later it was reported the device was inside the shrine itself. Bomb disposal specialists checked for secondary devices. It's not clear if any were found.

Eric Seldin was in a hotel across the road when the blast happened.

ERIC SELDIN, Local Journalist:

I was eating my noodles, and I literally shook from my shoulders. And the other patrons were extremely startled. Even the staff at the hotel were startled, because they had never heard anything like that.

DAN RIVERS:

The Ratchaprasong crossroads has been the scene of numerous violent protests in recent years involving competing factions in Thailand's long-running political instability that saw the army take power last year.

It's not clear if today's blast was linked to that political conflict or whether Islamist militants in Thailand's far south are to blame. But the effect on Thailand's tourism industry will be serious, hitting a place many Westerners visit with such devastating force.

JUDY WOODRUFF:

There was no immediate claim of responsibility for the attack.

China ordered a national check of workplace safety today, five days after explosions shattered the port of Tianjin and left 114 people dead. More teams were dispatched to search for at least another 70 still missing. Meanwhile, officials confirmed there were 700 tons of toxic sodium cyanide at the site, but said they have acted to prevent chemical runoff.

We are closely monitoring. The presence of spread of chemicals is not very bad. In terms of the situation after the rainfall, we still haven't seen any rainfall, but we have already made a precautionary plan to closely monitor. So, please, don't worry about it.

JUDY WOODRUFF:

Separately, foreign companies, including Toyota and Panasonic, moved to suspend operations around the port.

An aerial search in Indonesia has spotted the wreckage of a commercial airliner that crashed yesterday, but there's no word of survivors. The Trigana Air Service turboprop was found in a rugged area of the province of Papua. Relatives of the 54 people on board gathered at the airline's offices today. They will be taken to the crash site to identify remains of their loved ones. The plane also carried nearly $470,000 in government fuel aid for the poor.

Iran's supreme leader, Ayatollah Khamenei, said today that the fate of a nuclear deal lies with U.S. and Iranian lawmakers. He took no direct stance on the agreement himself. Instead, in a statement posted online, Khamenei said: "It is not clear if it will be approved here or there."

In Syria, government planes kept up an assault on the city of Duma, northeast of Damascus. Just yesterday, air raids in the rebel-held area left nearly 100 people dead and wounded hundreds more. The attacks also drew condemnation today from the White House and from a visiting U.N. humanitarian chief.

STEPHEN O’BRIEN, United Nations Humanitarian Chief:

I am absolutely horrified by the total disregard for civilian life by all parties in this conflict. Attacks on civilians are unlawful, unacceptable and must stop. I appeal to every party engaged in violence and fighting to protect civilians.

JUDY WOODRUFF:

Damascus has seen escalating violence in recent days, with attacks killing dozens last week as well.

Back in this country, the National Labor Relations Board has barred Northwestern University football players from forming the first union for college athletes. They wanted to negotiate shares of ticket sales and licensing deals. The NLRB said having union and non-union teams play each other could unbalance college sports.

The White House announced new steps today to battle a rise in the fatal overdoses of heroin. The $5 million plan will pair drug intelligence officials with public health workers to stop the drug's spread and to promote treatment. Heroin overdose deaths have quadrupled in the U.S. over the last decade.

Royal Dutch/Shell now has the green light to drill for oil off Alaska's northwest coast for the first time since 1991. Federal officials issued the final permit today.

And on Wall Street, the Dow Jones industrial average gained nearly 70 points to close at 17545. The Nasdaq rose more than 40 points, and the S&P 500 added 11.

And Emma Didlake, who was the Michigan woman believed to be the nation's oldest veteran, has died. She served as an Army driver during World War II. Just last month, Didlake met with President Obama, and he praised her today as a true trailblazer. Emma Didlake was 110 years old.